In the manufacture of many pharmaceutical products such as pills or lozenges, candies such as "M&M's", small mechanical parts such as ball bearings or electrical components such as resistors or capacitors, it is often desirable to imprint a trademark, indicia or other information or intelligence on each item. These products share a common characteristic in that they are all pellet-like items, being small, often round or rounded, oval, bulbous, cylindrical or polygonal in shape. Examples of pellet-like items are pills, lozenges, capsules, tablets and caplets.
Imprinting indicia on a series of pellet-like items is conveniently accomplished by a machine which receives a large number of items in bulk, typically from a feed hopper or bin, orients the items to a uniform relative orientation, conveys the oriented items to a printing unit wherein the indicia are applied to each item and discharges the items for subsequent packaging. U.S. Pat. No. 2,859,689 to Ackley is a typical example of a pellet marking machine which performs the steps outlined above. Pellet-like items, designated "P" in FIG. 2 of the '689 patent, are loaded in bulk into the feed hopper 22 where the items are received by a rotating drum or cylinder roll 23. The drum has a multiplicity of concavities or recesses 33 in its outwardly facing surface formed in accordance with the shape and size of the pellet-like items being processed. The items P are received into the concavities 33 as the drum rotates clockwise beneath hopper 22, retained in the concavities by cylindrical retainer surface 50 as the drum rotates and released to an endless conveyor 24 located beneath the drum, the conveyor having a multiplicity of individual carrier bars 110. Carrier bars 110 have corresponding concavities matching the concavities 33 in drum 23, and conveyor 24 is synchronized with drum 23 so that the matching concavities on the drum and the conveyor line up as the drum rotates clockwise and the conveyor circulates counterclockwise. Items P drop from concavities 33 in drum 23 into the matching concavities in the endless conveyor 24 once the items are clear of retaining surface 50. The pellet-like items P are then conveyed to a printing roller 27 which has ink laden images of the indicia or intelligence to be imprinted on the items circumferentially arrayed on its peripheral surface. Printing roller 27 rotates clockwise in synchronization with endless conveyor 24 and contacts the pellet-like items P as they pass beneath the printing roller 27, applying the ink laden image to each pellet-like item. After passing beneath printing roller 27, the pellet-like items P are discharged from conveyor 24 as the conveyor rounds its drive sprocket and the carrier bars 110 are momentarily vertically oriented.
Although pellet marking machines similar to that described in the '689 patent provide an effective means for reliably and rapidly marking pellet-like items with indicia, the machines are expensive and lack versatility, largely due to the design of rotating drum 23.
The drums are expensive because they are typically manufactured from a single custom made centrifugal casting which can weigh in excess of 350 lbs. This monolithic design has traditionally been thought necessary for drum manufacture in order to create a shell structure with a precision made, continuous outer surface which simultaneously allows access to the back surface of the shell for the mounting of auxiliary systems, such as vacuum assist systems to retain the pellet-like items to the drum as they are received from the hopper. The concavities are machined into the casting's curved outer surface, and machining such a heavy, monolithic piece is complicated, expensive, time consuming and risky. Complications arise because it is inherently more difficult to perform precision machining on a curved surface as compared with a flat surface, for example. The machining process is more expensive because often special tooling or jigs must be designed and fabricated to hold the heavy, bulky drum within the milling machine. The process is time consuming because of the typically large number of concavities which must be machined into a drum surface, requiring the drum to be constantly repositioned by the machinist on the milling machine so that the milling tool can have access to a tangent region on the drum surface. The process is risky because a single machining error can render the entire casting useless, perhaps negating many man-hours of machining effort, wasting thousands of dollars in material costs, as well as having an adverse impact on the production schedule for the machine.
In the recent past, pellet marking machine versatility was not a concern because there were a relatively limited number of pellet shapes and sizes in the marketplace and manufacturers by and large were satisfied with a dedicated machine for a particular product line. However, as the various industries, most notably pharmaceuticals, evolved over time, pellet marking machine versatility became more important. To remain competitive in the marketplace, pellet marking machines have been forced to evolve to keep up with the faster pace of technological change in product development, encapsulation methods, marking methods and packaging requirements, in addition to meeting the needs for greater efficiency and lower cost imposed by the highly competitive markets. In this context, pellet marking machine versatility, as evidenced by the ability to process different types of pellet-like items, has come to the fore as the desirable characteristic which makes one pellet marking machine superior to another among the various industrial customers.
The pellet marking machines of the past lack versatility because a monolithic drum can only have one type of concavity with a predetermined size and shape machined into its outer surface. The concavities in the monolithic drum must be specifically matched in size and shape to the particular pellet-like item being processed. Matching the concavity to the item is important for efficient processing of the items by the machine. Items which are poorly matched to their receiving concavities will not be efficiently received from the hopper, reducing the efficiency and item throughput of the machine as some concavities will fail to pick up an item as they pass beneath the hopper. The empty concavities have no item to transfer to the conveyor as the drum rotates through its cycle, resulting in an empty conveyor cavity passing beneath the printing rollers. Items which are received into concavities on the drum but which are not consistently positioned and reliably held due to shape or size mismatch between the items and the concavities will not be reliably and consistently transferred to the conveyor. Items not positioned precisely on the conveyor will not be correctly imprinted when the items pass beneath the printing roller, resulting in an unacceptable product and costly wastage. Some products may not make it to the printing roller at all and could even end up rolling loose on the conveyor, falling from the conveyor onto the factory floor or into the machine and fouling its moving parts.
Thus, if it is desired to process more than one type of pellet-like article with the same machine, a separate monolithic drum must be made to match to each type of item. Due to the size and weight of the monolithic drum and its position within the machine, a significant part of the machine must be disassembled to effect the change over to the new drum. The change over can require significant manpower as it is difficult for one person to safely handle a heavy drum and can further entail significant machine down time, adversely affecting item production rates and schedules. Furthermore, if a monolithic drum becomes damaged, it cannot be readily repaired in situ. Repair will typically require extensive machine down time to disassemble the machine and remove the drum for repair or replacement. Clearly, there is a need for an improved drum design in pellet marking machines which will increase versatility and efficiency of the machines while reducing the cost and risks associated with machine manufacture.